1. Field of the Invention
The present invention relates to a method for effective network selection by a wireless terminal in a heterogeneous network environment, and more particularly to a method for a more efficient selection by a wireless terminal between a mobile communication network and a wireless local area network (WLAN) in a heterogeneous network environment.
2. Description of the Related Art
Conventional mobile communication networks are classified into a frequency division multiple access (FDMA) scheme, a time division multiple access (TDMA) scheme and a code division multiple access (CDMA) scheme according to their communication methods. The FDMA scheme allows each subscriber to use a frequency channel allocated a wireless terminal to by dividing the frequency band into a plurality of channels. The TDMA scheme allows a plurality of wireless terminals to use one frequency channel through time division. The CDMA scheme allows a plurality of wireless terminals to communicate through the same frequency band at the same time by using different codes allocated to the wireless terminals.
With the rapid development of communication technology, the current mobile communication networks have come to provide mobile terminals with a fast data service capable of transmitting mail, still pictures, and multimedia services such as moving pictures, as well as the conventional voice communication service. Third generation (3G) mobile communication systems capable of supporting both conventional voice communication service and packet service include a synchronous CDMA 2000 1x system and an asynchronous universal mobile telecommunication system (UMTS).
In addition, extensive research is being conducted into wireless networks, such as a WLAN, a wireless broadband Internet (WiBro) to provide a mobile Internet service using a frequency of 2.3 GHz, etc.
Connecting systems between the mobile communication network and the WLAN has have been developed, so that it is possible to efficiently provide a multimedia service. The 3rd Generation Partnership Project (3GPP), which is a standardization organization for the mobile communication system, classifies the connecting systems into two types of systems according to a coupling point for the connection between the mobile communication network and the WLAN. One of the two types of connecting systems is a loosely-coupled system in which a WLAN is coupled to an interface between a gateway General Packet Radio (GPRS) support node (GGSN) and an external Internet Protocol (IP) Internet, and the other is a tightly-coupled system in which a WLAN is coupled to a serving GPRS support node (SGSN)/packet control function (PCF), which corresponds to a core network of a mobile communication network.
When a multimedia data service is provided by using the above-mentioned connecting systems between the mobile communication network and the WLAN, a wireless terminal performs selection between an interface of the mobile communication network and an interface of the WLAN. In this case, the wireless terminal selects either the interface of the mobile communication network or the interface of WLAN according to weight values of the interfaces.
The weight value of each interface is calculated by a sum of a power of a received signal from an accessible interface and a priority of the interface, which can be expressed by Equation (1)W=1000×PW+Pr  (1)
In Equation (1), “W” represents the weight value of a corresponding interface, and “PW” represents a reception power. In addition, “Pr” represents the priority of the corresponding interface. The priorities of interfaces may differ depending on each wireless device. For example, in the case of a wireless terminal in which the main purpose is providing a voice service, a mobile communication network has a higher priority (e.g. 1000) than that (e.g. 800) of a WLAN.
When the wireless terminal selects and uses either the interface of the mobile communication network or the interface of the WLAN based on the weight values of the interfaces calculated using Equation (1), transmission of data may be delayed or interrupted because a difference between the available data rates of the heterogeneous networks has not been considered. In addition, there is a problem in that, even when the reception power from the WLAN is only slightly less than the reception power from the mobile communication network, the less expensive WLAN will not be selected but the more expensive mobile communication network will be selected.